ZGC is part of OpenJDK and licensed under GPL.
This can also destroy investment rounds for many startups.
They could sue you, with a higher chance of winning, for using a python, a js or a ruby than for using OpenJDK derived code.
Do you happen to know of any real-world case that's similar to the scenario you've described?
They only support part of the standard library, the OpenJDK parts have been cherry picked and not all are made available on the same Android version and then there are the bytecodes that were introduced since Java 7.
And for Java language support, you need to have Android Oreo version of ART as not all language features get desugared into older versions.
There is some AOSP activity related to Java 9, but so far Google has been silent if there will be any further improvements beyond Java 8.